There has been known one type of T-nut, as disclosed, for example, in Japanese Patent Laid-Open Publication No. H04-341606 or H06-323315. These T-nuts include a shank having a thin-walled portion to be caulked or crimped. Specifically, a T-nut 11 disclosed in the above Japanese Patent Laid-Open Publication No. H04-341606 has a shape as shown in FIGS. 23(a) and 23(b), and comprises a shank 12 and a flange 13 extending from outward from a first end of the shank 12. The shank 12 and the flange 13 can be integrally formed, for example, by processing an iron-based metal sheet.
The shank 12 has a hollow tubular shape with an even outer diameter. The shank 12 includes a portion 14 to be crimped (hereinafter referred to as “crimpable portion”) at a second end of the shank on the other side of the first end, and an internally threaded portion 15, or the remaining portion of the shank 12 other than the crimpable portion 14, which has an internal thread 15a formed in the inner peripheral surface thereof. The crimpable portion 14 has a thinner wall than that of the internally threaded portion 15. Thus, in a machining process of forming the internal thread 15a, a thread cutting operation can be performed from either side of the first and second ends of the shank 12.
The flange 13 includes a pair of pawls 16 formed by pressing a part of the outer peripheral edge of the flange 13 in the inward direction from the outside. The pair of pawls 16 protrude toward the second end of the shank 12 while being opposed to one another at 180-degree. As a result of forming the pawls 16, a pair of corresponding notches 17 each having an approximately semicircular cross-section are left in the outer peripheral edge of the flange 13.
The above T-nut 11 is used in its fixed state, for example, as shown in FIG. 24(a). Referring to FIG. 24(a), the shank 12 is first inserted into a through-hole 18 which is formed in advance in a workpiece 19 made resin material or wood, and then the crimpable portion 14 is crimped by a crimping machine to form a crimped portion 14a on the side of one of the surfaces of the workpiece 19. Through this crimpable operation, the pawls 16 are also driven to bite into the other surface of the workpiece 19. In this way, an operation of fixing the T-nut 11 to the workpiece 19 is completed.
A T-nut 31 disclosed in the above Japanese Patent Laid-Open Publication No. H06-323315 has a shape as shown in FIGS. 25(a) and 25(b), and comprises a shank 32 and a flange 33 extending from outward from a first end of the shank 32. The shank 32 and the flange 33 can be integrally formed, for example, by processing an iron-based metal sheet. The shank 32 includes an internally threaded portion 35 having an internal thread 36 formed in the inner peripheral surface of the shank, and a crimpable portion 34. The structure of the T-nut 33 is different from that of the aforementioned T-nut 11 in that the outer peripheral portion of the flange 33 is formed with two pairs of pawls 37/38 and 39/40 disposed opposed to one another in the radial direction of the flange 33 and each extending from a first end toward a second end of the shank 32, and the flange 33 has a substantially octagonal shape in its entirety.
This T-nut 31 is generally referred to as “hopper feed T-nut”, because the T-nut can be smoothly moved along a feed track of a nut setter for fixedly setting the T-nut 31 to a workpiece to allow the nut setter to automatically feed the T-nuts. The detail of one type of the hopper feed T-nut is disclosed in British Patent No. 1,157,734.
The T-nut 31 is used in the same fixed state as that of the T-nut 11, for example, as shown in FIG. 24(b). Specifically, the shank 32 of the T-nut 31 is inserted into a through-hole 18 of a workpiece 19, and then the crimpable portion 34 is crimped by a crimping machine to form a crimped portion 34a on the side of one of the surfaces of the workpiece 19. Simultaneously, the pawls 37-40 are driven to bite into the other surface of the workpiece 19.
In the fixed state of the T-nut 31, the pawls 37-40 prevent the T-nut 31 from being rotated relative to the workpiece 19, and the flange 33 and the crimped portion 34a cramps the workpiece 19 therebetween to prevent the T-nut 31 from escaping from the through-hole 18. Thus, the T-nut 31 is firmly fixed to the workpiece 19, and this fixed state will be semi-permanently maintained.
Another type of T-nut having no crimpable portion is fixed through the same operation except for the crimpable process.
After the T-nut 11, 31 is fixed to the workpiece 19 as shown in FIGS. 24(a) and 24(b), one surface 19A of the workpiece 19 is applied with a liquid such as oil or paint, or is immersed into the liquid, in some cases.
In such a case, the liquid, such as oil or paint, can enter in an opening portion 11A, 31A of the T-nut 11, 31 at the first end thereof. The liquid which has entered in the opening portion 11A, 31A of the T-nut 11, 31 should be removed in view of its adverse affect on subsequent operations and quality maintenance. However, if the liquid which has entered from the opening portion into the inside of the shank is removed for each of a number of T-nuts, it will be an extremely inefficient and time-consuming operation.